<template>
  <div class="spec-preview">
    <img :src="imgObj.imgUrl" />
    <div class="event" @mousemove="moveMask"></div>
    <div class="big">
      <img :src="imgObj.imgUrl" ref="big"/>
    </div>
    <div class="mask" ref="mask"></div>
  </div>
</template>

<script>
  export default {
    name: "Zoom",
    data(){
      return {
         //大图的索引值
         bigIndex:0
      }
    },
    //父亲给的至少是一个空数组
    props:['imageList'],
    computed:{
      //图片路径地址
      imgObj(){
       return this.imageList[this.bigIndex]||{};
      }
    },
    mounted(){
      this.$bus.$on('sendIndex',(index)=>{
            //修改大图的索引值
            this.bigIndex = index;
      })
    },
    methods: {
      //鼠标移动的回调
      moveMask(event){
        //获取蒙板DOM:定位元素，可以通过JS实现动态修改left、top实现拖拽效果
        let mask  = this.$refs.mask;
        //获取右侧的大图
        let big = this.$refs.big;
        //计算蒙板的left与top数值
        let x = event.offsetX - mask.offsetWidth/2;
        let y = event.offsetY - mask.offsetHeight/2;
        //约束x与y数值范围
        if(x<=0) x = 0;
        if(x>=mask.offsetWidth) x = mask.offsetWidth;
        if(y<=0) y=0;
        if(y>=mask.offsetHeight) y = mask.offsetHeight;
        //修改蒙板的left与top数值
        mask.style.left = x+'px';
        mask.style.top = y +'px';
        //修改大图的left与top
        big.style.left = -2 * x +'px';
        big.style.top = -2 * y +"px";
      }
    }

  }
</script>

<style lang="less">
  .spec-preview {
    position: relative;
    width: 400px;
    height: 400px;
    border: 1px solid #ccc;

    img {
      width: 100%;
      height: 100%;
    }

    .event {
      width: 100%;
      height: 100%;
      position: absolute;
      top: 0;
      left: 0;
      z-index: 998;
    }

    .mask {
      width: 50%;
      height: 50%;
      background-color: rgba(0, 255, 0, 0.3);
      position: absolute;
      left: 0;
      top: 0;
      display: none;
    }

    .big {
      width: 100%;
      height: 100%;
      position: absolute;
      top: -1px;
      left: 100%;
      border: 1px solid #aaa;
      overflow: hidden;
      z-index: 998;
      display: none;
      background: white;

      img {
        width: 200%;
        max-width: 200%;
        height: 200%;
        position: absolute;
        left: 0;
        top: 0;
      }
    }

    .event:hover~.mask,
    .event:hover~.big {
      display: block;
    }
  }
</style>